Comparative assessment of intimal hyperplasia development after 14 days in two different experimental settings: tissue culture versus ex vivo continuous perfusion of human saphenous vein

Biomechanical properties of veins cultured in vitro under elevated internal pressure

BACKGROUND

The venous response to elevated blood pressure (BP) is of major importance because it is closely related to the etiology of venous diseases and the competency of vein grafts. In vitro culture experiments may provide useful information on the function of vein grafts because it is easier to separate mechanical and hemodynamic effects from other systemic influences compared to in vivo experiments.

OBJECTIVE

To study the effects of BP elevation on wall dimensions and mechanical properties of in vitro cultured veins.

METHODS

Rabbit femoral veins were cultured in vitro under internal pressures of 1 to 50 mmHg for 1 week, and their wall dimensions, biomechanical properties, and histology were determined.

RESULTS

No significant differences were observed in internal vein diameter and wall thickness among vessels cultured at 10-50 mmHg compared to non-cultured control vessels. For an internal pressure of 10 mmHg applied to vessels during culture (equivalent to in vivo working BP), wall circumferential stress was maintained within control levels. There were no significant effects of pressure on basal tone and contractility of vascular smooth muscle and vascular compliance.

CONCLUSIONS

The in vitro results were essentially similar to those obtained from previous in vivo animal experiments, indicating that in vitro tissue culture techniques are applicable to studies of venous remodeling.

Human Saphenous Vein Response to Trans-wall Oxygen Gradients in a Novel Ex Vivo Conditioning Platform

Autologous saphenous veins are commonly used for the coronary artery bypass grafting even if they are liable to progressive patency reduction, known as 'vein graft disease'. Although several cellular and molecular causes for vein graft disease have been identified using in vivo models, the metabolic cues induced by sudden interruption of vasa vasorum blood supply have remained unexplored. In the present manuscript, we describe the design of an ex vivo culture system allowing the generation of an oxygen gradient between the luminal and the adventitial sides of the vein. This system featured a separation between the inner and the outer vessel culture circuits, and integrated a purpose-developed de-oxygenator module enabling the trans-wall oxygen distribution (high oxygen level at luminal side and low oxygen level at the adventitial side) existing in arterialized veins. Compared with standard cultures the bypass-specific conditions determined a significant increase in the proliferation of cells around adventitial vasa vasorum and an elevation in the length density of small and large caliber vasa vasorum. These results suggest, for the first time, a cause-effect relationship between the vein adventitial hypoxia and a neo-vascularization process, a factor known to predispose the arterialized vein conduits to restenosis.

Role of hemodynamic forces in the ex vivo arterialization of human saphenous veins

BACKGROUND

Human saphenous vein grafts are one of the salvage bypass conduits when endovascular procedures are not feasible or fail. Understanding the remodeling process that venous grafts undergo during exposure to arterial conditions is crucial to improve their patency, which is often compromised by intimal hyperplasia. The precise role of hemodynamic forces such as shear stress and arterial pressure in this remodeling is not fully characterized. The aim of this study was to determine the involvement of arterial shear stress and pressure on vein wall remodeling and to unravel the underlying molecular mechanisms.

METHODS

An ex vivo vein support system was modified for chronic (up to 1 week), pulsatile perfusion of human saphenous veins under controlled conditions that permitted the separate control of arterial shear stress and different arterial pressure (7 mm Hg or 70 mm Hg).

RESULTS

Veins perfused for 7 days under high pressure (70 mm Hg) underwent significant development of a neointima compared with veins exposed to low pressure (7 mm Hg). These structural changes were associated with altered expression of several molecular markers. Exposure to an arterial shear stress under low pressure increased the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1 at the transcript, protein, and activity levels. This increase was enhanced by high pressure, which also increased TIMP-2 protein expression despite decreased levels of the cognate transcript. In contrast, the expression of plasminogen activator inhibitor-1 increased with shear stress but was not modified by pressure. Levels of the venous marker Eph-B4 were decreased under arterial shear stress, and levels of the arterial marker Ephrin-B2 were downregulated under high-pressure conditions.

CONCLUSIONS

This model is a valuable tool to identify the role of hemodynamic forces and to decipher the molecular mechanisms leading to failure of human saphenous vein grafts. Under ex vivo conditions, arterial perfusion is sufficient to activate the remodeling of human veins, a change that is associated with the loss of specific vein markers. Elevation of pressure generates intimal hyperplasia, even though veins do not acquire arterial markers.

CLINICAL RELEVANCE

The pathological remodeling of the venous wall, which leads to stenosis and ultimately graft failure, is the main limiting factor of human saphenous vein graft bypass. This remodeling is due to the hemodynamic adaptation of the vein to the arterial environment and cannot be prevented by conventional therapy. To develop a more targeted therapy, a better understanding of the molecular mechanisms involved in intimal hyperplasia is essential, which requires the development of ex vivo models of chronic perfusion of human veins.

Pulsatile ex vivo perfusion of human saphenous vein grafts under controlled pressure conditions increases MMP-2 expression

Background

The use of human saphenous vein grafts (HSVGs) as a bypass conduit is a standard procedure in the treatment of coronary artery disease while their early occlusion remains a major problem.

Methods

We have developed an ex vivo perfusion system, which uses standardized and strictly controlled hemodynamic parameters for the pulsatile and non-static perfusion of HSVGs to guarantee a reliable analysis of molecular parameters under different pressure conditions. Cell viability of HSVGs (n = 12) was determined by the metabolic conversion of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) into a purple formazan dye.

Results

Under physiological flow rates (10 mmHg) HSVGs remained viable for two weeks. Their exposure to arterial conditions (100 mmHg) was possible for one week without important reduction in viability. Baseline expression of matrix metalloproteinase-2 (MMP-2) after venous perfusion (2.2 ± 0.5, n = 5) was strongly up-regulated after exposure to arterial conditions for three days (19.8 ± 4.3) or five days (23.9 ± 6.1, p < 0.05). Zymographic analyses confirmed this increase on the protein level. Our results suggest that expression and activity of MMP-2 are strongly increased after exposure of HSVGs to arterial hemodynamic conditions compared to physiological conditions.

Conclusion

Therefore, our system might be helpful to more precisely understand the molecular mechanisms leading to an early failure of HSVGs.

Cyclic nucleotide phosphodiesterase 1 regulates lysosome-dependent type I collagen protein degradation in vascular smooth muscle cells

OBJECTIVE

The phenotypic modulation of vascular smooth muscle cells (VSMCs) to a synthetic phenotype is vital during pathological vascular remodeling and the development of various vascular diseases. An increase in type I collagen (collagen I) has been implicated in synthetic VSMCs, and cyclic nucleotide signaling is critical in collagen I regulation. Herein, we investigate the role and underlying mechanism of cyclic nucleotide phosphodiesterase 1 (PDE1) in regulating collagen I in synthetic VSMCs.

METHODS AND RESULTS

The PDE1 inhibitor IC86340 significantly reduced collagen I in human saphenous vein explants undergoing spontaneous remodeling via ex vivo culture. In synthetic VSMCs, high basal levels of intracellular and extracellular collagen I protein were markedly decreased by IC86340. This attenuation was due to diminished protein but not mRNA. Inhibition of lysosome function abolished the effect of IC86340 on collagen I protein expression. PDE1C but not PDE1A is the major isoform responsible for mediating the effects of IC86340. Bicarbonate-sensitive soluble adenylyl cyclase/cAMP signaling was modulated by PDE1C, which is critical in collagen I degradation in VSMCs.

CONCLUSIONS

These data demonstrate that PDE1C regulates soluble adenylyl cyclase/cAMP signaling and lysosome-mediated collagen I protein degradation, and they suggest that PDE1C plays a critical role in regulating collagen homeostasis during pathological vascular remodeling.

Design and Subspace System Identification of an Ex Vivo Vascular Perfusion System

Numerical algorithms for subspace system identification (N4SID) are a powerful tool for generating the state space (SS) representation of any system. The purpose of this work was to use N4SID to generate SS models of the flowrate and pressure generation within an ex vivo vascular perfusion system (EVPS). Accurate SS models were generated and converted to transfer functions (TFs) to be used for proportional integral and derivative (PID) controller design. By prescribing the pressure and flowrate inputs to the pumping components within the EVPS and measuring the resulting pressure and flowrate in the system,_four TFs were estimated;_two for a flowrate controller (HRP,f and HRPP,f) and two for a pressure controller (HRP,p and HRPP,p). In each controller,_one TF represents a roller pump (HRP,f and HRP,p),_and the other represents a roller pump and piston in series (HRPP,f and HRPP,p). Experiments to generate the four TFs were repeated five times (N=5) from which average TFs were calculated. The average model fits, computed as the percentage of the output variation (to_the_prescribed_inputs) reproduced by the model, were 94.93±1.05% for HRP,p, 81.29±0.20% for HRPP,p, 94.45±0.73% for HRP,f, and 77.12±0.36% for HRPP,f. The simulated step, impulse, and frequency responses indicate that the EVPS is a stable system and can respond to signals containing power of up to 70_Hz.

Increased connexin43 expression in human saphenous veins in culture is associated with intimal hyperplasia

OBJECTIVE

Intimal hyperplasia is a vascular remodelling process that occurs after a vascular injury. The mechanisms involved in intimal hyperplasia are proliferation, dedifferentiation, and migration of medial smooth muscle cells towards the subintimal space. We postulated that gap junctions, which coordinate physiologic processes such as cell growth and differentiation, might participate in the development of intimal hyperplasia. Connexin43 (Cx43) expression levels may be altered in intimal hyperplasia, and we therefore evaluated the regulated expression of Cx43 in human saphenous veins in culture in the presence or not of fluvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity.

METHODS

Segments of harvested human saphenous veins, obtained at the time of bypass graft, were opened longitudinally with the luminal surface uppermost and maintained in culture for 14 days. Vein fragments were then processed for histologic examination, neointimal thickness measurements, immunocytochemistry, RNA, and proteins analysis.

RESULTS

Of the four connexins (Cx37, 40, 43, and 45), we focused on Cx43 and Cx40, which we found by real-time polymerase chain reaction to be expressed in the saphenous vein because they are the predominant connexins expressed by smooth muscle cells and endothelial cells. After 14 days of culture, histomorphometric analysis showed a significant increase in the intimal thickness as observed during the process of intimal hyperplasia. A time-course analysis revealed a progressive upregulation of Cx43 to reach a maximal increase of sixfold to eightfold at both transcript and protein levels after 14 days in culture. In contrast, the expression of Cx40, abundantly expressed in the endothelial cells, was not altered. Immunofluorescence showed a large increase in Cx43 within smooth muscle cell membranes of the media layer. The development of intimal hyperplasia in vitro was decreased in presence of fluvastatin and was associated with reduced Cx43 expression.

CONCLUSIONS

These data show that Cx43 is increased in vitro during the process of intimal hyperplasia and that fluvastatin could prevent this induction, supporting a critical role for Cx43-mediated gap-junctional communication in the human vein during the development of intimal hyperplasia.

CLINICAL RELEVANCE

Stenosis due to intimal hyperplasia is the most common cause of failure of venous bypass grafts. To better understand the development of intimal hyperplasia, we used an ex vivo organ culture model to study saphenous veins harvested from patients undergoing a lower limb bypass surgery. In this model, the morphologic and functional integrity of the vessel wall is maintained and significant intimal hyperplasia development occurs after 14 days in culture. We have postulated that gap junctions, which coordinate physiologic processes such as cell growth and differentiation, may participate in the development of intimal hyperplasia. Indeed, intimal hyperplasia consists of proliferation and migration of smooth muscle cells into the subendothelial space. Intercellular communication is responsible for the direct transfer of ions and small molecules from one cell to the other through gap-junction channels found at cell-cell appositions. No study to date has evaluated whether gap junctional communication is involved in the process of intimal hyperplasia in humans. This assertion was investigated by using the aforementioned organ culture model of intimal hyperplasia in human saphenous veins, and our data support a critical role for Cx43-mediated gap junctional communication in human vein during the development of intimal hyperplasia.

Peyronie’s disease associated with increase in plasminogen activator inhibitor in fibrotic plaque

OBJECTIVES

To investigate whether tissue expression of plasminogen activator inhibitor type 1 (PAI-1) is increased in the fibrotic plaque of human Peyronie's disease (PD). Increased tissue levels of PAI-1, an inhibitor of both fibrinolysis and collagenolysis, have been found in a variety of fibrotic conditions. Recently, it was reported that PAI-1 expression was also increased in the fibrotic plaque of an animal model of PD induced by the injection of fibrin into the tunica albuginea (TA) of the penis.

METHODS

Tissue (n = 10/group) and cells (n = 4/group) obtained from the penile TA plaque of patients with PD or from normal TA were subjected to RNA extraction and real-time reverse transcriptase-polymerase chain reaction. Tissues were also analyzed by immunohistochemistry (n = 8/group) for the detection of PAI-1 expression at the transcription and protein levels.

RESULTS

A significant 3.5-fold to 16-fold increase was found in both PAI-1 mRNA and protein levels in the human PD plaque and the respective fibroblast cultures compared with the normal non-PD TA.

CONCLUSIONS

The observed increase in PAI-1 in the human PD plaque agrees with what has been observed in the rat and suggests that PAI-1 may be a key pro-fibrotic factor in the development of human PD.

Improvement of Function and Morphology of Tumor Necrosis Factor-.ALPHA. Treated Endothelial Cells With 17-.BETA. Estradiol A Preliminary Study for a Feasible Simple Model for Atherosclerosis

BACKGROUND

Dysfunction of endothelial cells (EC) to produce endothelial nitric oxide synthase (eNOS) by tumor necrosis factor-alpha (TNF-alpha) causes critical features of vascular inflammation associated with several disease states (eg, atherosclerosis including increased platelet aggregation and adhesion on EC, elevated adhesion molecules and enhanced inflammatory cells binding to EC). 17-beta estradiol (E2) can stimulate eNOS production and improve the critical features of atherosclerosis. Using TNF-alpha and E2, we attempted to develop an in vitro vascular model for studying atherosclerosis.

METHODS AND RESULTS

Human umbilical vein endothelial cells (HUVEC) grown in transwells were cocultured with smooth muscle cells in a 24-well plate to mimic the major components of the vascular wall. The model was incubated with TNF-alpha (10 ng/ml) for 12 h, prior exposed to E2 (100 pg/ml) for 6-12 h, then investigated by transmission and scanning electron microscopes. The result indicated recovered morphology with good tight junction, and decreased platelet adhesion was noted in defective HUVEC after E2 treatment.

CONCLUSION

17-beta estradiol was represented as an antiatherosclerogenic agent to demonstrate feasibility of the model. Although our finding focused only on the endothelium, this would be the basis for our future studies to develop ex vivo continuous perfusion of human vessel segments for a further atherosclerosis study.